Topband: Apparent Multiple Resonances on a single antenna

[Sinisa Hristov]

Bill wrote:
 
> I seem to recall reading on this reflector that it is possible to find
> multiple resonant points on a single antenna.  Measuring my shortened
> 160m vertical, I find resonances at every now and all the way up through
> low VHF using an antenna analyzer.
 
> For instance, I found almost a 1:1 match on 71.29mhz and other close matches
> as I moved down to 160m.  How is this possible and where is this coming from?

> I believe it is from the surrounding physical clutter to the vertical that
> is providing these seemingly multiple resonant points.  I also noticed the
> same thing on an 80 meter vertical I had constructed at one time.
> Anyone with an answer to this?


If your antenna is properly fed with a good balun,
you'd get resonances on odd harmonics with SWR
generally increasing with frequency due to
increasing radiation resistance. This implies that
both radials and balun are functional over entire
frequency range, which most likely doesn't hold.

Without a balun, or with a bad one, you'd also
get resonances from the entire system = coax + balun + antenna.
Such resonances are unpredictable.


73,

Sinisa  YT1NT, VA3TTN